NEN EN ISO 4126-1 : 2013 AMD 1 2016

1 Scope
2 Normative references
3 Terms and definitions
4 Symbols and units
5 Design
   5.1 General
   5.2 End connections
   5.3 Minimum requirements for springs
   5.4 Materials
6 Production testing
   6.1 Purpose
   6.2 General
   6.3 Hydrostatic testing
   6.4 Pneumatic testing
   6.5 Adjustment of cold differential test pressure
   6.6 Seat leakage test
7 Type testing
   7.1 General
   7.2 Tests to determine operating characteristics
   7.3 Tests to determine flow characteristics
   7.4 Determination of the coefficient of discharge
   7.5 Certification of coefficient of discharge
8 Determination of safety valve performance
   8.1 Determination of coefficient of discharge
   8.2 Critical and subcritical flow
   8.3 Discharge capacity at critical flow
   8.4 Discharge capacity for any gas at subcritical flow
   8.5 Discharge capacity for non-flashing liquid as the
        test medium in the turbulent zone where the Reynolds
        number R[e] is equal to or greater than 80000
9 Sizing of safety valves
   9.1 General
   9.2 Valves for gas or vapour relief
   9.3 Calculation of capacity
10 Marking and sealing
   10.1 Marking on the shell of a safety valve
   10.2 Marking on an identification plate
   10.3 Sealing of a safety valve
Annex A (informative) Examples of sizing calculations for
        various fluids
        A.1 Capacity calculations for gaseous media at critical
            flow
        A.2 Capacity calculations for gaseous media at subcritical
            flow
        A.3 Capacity calculations for liquids
Annex ZA (informative) Relationship between this European
         Standard and the Essential Requirements of EU
         Directive 97/23/EC (PED)
National Annex NA (informative) Performance testing of safety
                  valves for hot water duty
National Annex NB (informative) Supplementary information

Defines general requirements for safety valves irrespective of the fluid for which they are designed. Pertains to safety valves having a flow diameter of 4 mm and above which are for use at set pressures of 0,1 bar gauge and above.